Introduction to Forces Common Misconceptions Common Misconceptions about

Introduction to Forces: Common Misconceptions

Common Misconceptions about Forces True or False ____ When a ball has been thrown, the force of the hand that threw it remains on it ____ A force is needed to keep an object moving ____ Inertia is a force ____ Air does not exert a force ____ The quantity ma is a force

Common Misconceptions about Forces Short Answer If there is no net force the object will continue with ____ velocity (unchanged, increased, or decreased) Inertia is the tendency of an object to resist __________. (motion, change in motion, increase in motion, or decrease in motion) The force exerted by air is a ______ force. (small, balanced, or negative) The equation F= _____ is a mathematical model of Newton’s 2 nd Law.

Newton’s First Law of Motion ( The Law of Inertia) Homework: Read 4. 1 -4. 3 and be prepared for a brief quiz tomorrow

Aristotle and the Early Greeks (Around 300 B. C. ) ► Believed there were two types of motion and they were: Natural motion – objects were moving because they were moving toward their natural resting place Violent motion – imposed motion. This was the result of an object being pushed or pulled.

A More Modern View: Galileo Galilei (1564 -1642) Used his telescope to make such astronomical discoveries such as the rough surface of the moon, the four moons revolving around Jupiter, “sunspots”, the fact that the Milky Way is made up of a myriad of single, faraway stars and the phases of Venus. ► Used the Leaning Tower of Pisa as a laboratory to test his law of falling bodies. ► Was the first “scientist” because he used experiments to prove/disprove his ideas. ►

Galileo and His Ramp Experiment ► ► ► Galileo did an experiment with two ramps. The ball rolls down the incline and up the opposite incline and reaches almost its initial height. He replaced the second ramp with a longer, less-steep ramp and released the ball on the first ramp. The ball rolled further and up the second incline to almost the same height from where it was released. Hypothetically Galileo reasoned that if the second ramp was removed altogether, the ball would roll down the first incline plane and roll forever and ever trying to attain the same height from where it was released.

Comparison between Aristotle and Galileo ARISTOTLE ► Things at rest were at their natural resting place. ► Objects that are moving away from their natural resting place need to be continuously forced to keep them moving GALILEO ► Objects at rest stay at rest until something forces them to do otherwise. ► Objects in motion want to continue in motion unless something stops them.

Inertia ► Idea that Galileo came up with ► Derived from Latin meaning “idleness” or “laziness” ► Definition: an objects’ resistance to change its state of motion

Sir Isaac Newton ► Born on Christmas Day in 1642 ► Please see thumbnail sketch of his life ► “If I have been able to see further, it was only because I stood on the shoulders of giants. ”

Newtons 1 st Law of Motion (The Law of Inertia) ► Every object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it. ► In other words: § Objects at rest, stay at rest § Objects in motion, stay in motion. § UNLESS ACTED UPON BY AN OUTSIDE FORCE

Vocabulary terms ► Inertia – Tendency of an object to resist change in motion ► Equilibrium – an object is in equilibrium if it is at rest or moving with a constant velocity (note: rest is a constant velocity of zero). (For this to be achieved the NET force has to be zero, more about this later)

Vocabulary Terms continued ► contact forces – push or pull on an object through touching it (contact) ► Long range – push or pull on an object without direct contact ► Agents – cause of force (i. e. “applied”, gravity, “normal”, friction, … among others)

What gives an object a lot of Inertia? ► Is it volume? Volume – the amount of space an object takes up NO!!!!!!

What gives an object a lot of Inertia? ► Is it weight? Weight – the effect that gravity has on an object NO!!!!!!

What gives an object a lot of Inertia? ► Is it mass? Mass – the amount of matter an object possesses. -the amount of “stuff” something has YES!!!!!!!!!

Can you measure mass in space? Yes. Since astronauts are weightless during their mission, keeping track of their weight can not be accomplished by asking them to step on the traditional bathroom scale. They are strapped into a device called an inertial balance and vibrated back and forth. What would happen to the period of vibration if the astronaut losses mass? How about if he/she gains mass?

Concussions ► A concussion occurs when the brain collides with the skull and the result is bruising of the brain. Sometimes the person loses consciousness. New technology in the design of helmets helps to reduce the chance of a concussion occurring

Whiplash ► Whiplash is the term that is used when someone is struck from behind, either in a car, or not and the head stays at rest while the body moves forward causing the head to make a whipping motion.

Homework Assignment ► Due tomorrow, you are to find a specific example of Newton’s 1 st Law. Your example should… § be written in your notebook § include diagrams § be unique. Any duplications will receive a zero (0). Any examples discussed in class may not be used.

How do you change the state of motion of an object?

Apply a Force! Force- a push or a pull -measured in Newtons (N)

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